1. Field of the Invention
The present invention relates to chemical vapor deposition apparatus and, more particularly, to multi station sequential processing within a common chamber of one or multiple single substrates.
2. Description of the Prior Art
Plasma enhanced chemical vapor deposition (PECVD) methods have been developed relatively recently. Little literature is publicly available and much of that is directed to well known chemistry usable with PECVD rather than being directed to practical high throughput apparatus for implementing the process. PECVD uses an RF (radio frequency) induced gas discharge to transfer energy to the reactant gases which allows a substrate to remain at a lower temperature than other processes. Such lower substrate temperature is a significant advantage in that it permits a method of depositing films on substrates that do not have thermal stability to accept coating by other methods. Additionally, PECVD can enhance the deposition rate when compared to thermal reactions alone and produce films of unique compositions and properties. Because of properties such as good adhesion, low pinhole density, good step coverage, adequate electrical properties and compatibility with fine line pattern transfer processes, this process has been used in integrated circuit manufacturing.
There are primarily three types of PECVD reactors: parallel plate, horizontal tube and single wafer. In a parallel plate reactor, the substrates or wafers are supported on a bottom grounded electrode and RF power is applied to an upper electrode. The grounded electrode may be rotated and heated to enhance uniformity. The reactant gas flow may be introduced centrally and removed peripherally or the reverse. In a hollow tube PECVD reactor, a plurality of vertically oriented electrodes are stacked parallel with one another with alternating plates serving as the power and ground electrodes for the applied RF energy. The wafers are interleaved with the electrodes. Generally, the entire assembly must be withdrawn from the tube for loading and unloading.
A single wafer PECVD reactor may be load locked and offer cassette to cassette operation. Radiant heating of the wafer may be provided. The application of RF energy enhances the deposition process, as discussed above. An embodiment of this type of reactor includes a plurality of discrete gas dispersion heads disposed within a reactor for discharging a reactant gas to wafers disposed therebeneath upon a common plate. The use of such multiple heads provides a sequential station capability for deposition at each station.
The chemistry and operating parameters attendant the process described below and related chemical vapor deposition (CVD) processes are described in detail in a textbook entitled Silicon Processing For the VLSI Era, Volume I--Process Technology, by S. Wolf and R. N. Tauber, published by the Lattice Press of Sunset Beach, California in 1987; chapters 5 and 6 are noted in particular. Further related information has been published in an article entitled "Chemical Vapor Deposition Techniques" by T. M. Besmann, D. P. Stinton and R. A. Lowden in the November 1988 issue of MRS Bulletin and references cited therein.